Rotor centralization for turbine engine assembly

ABSTRACT

One or more support elements radially extend through one or more openings defined in a turbine engine casing and are configured to centralize and at least partially support a rotor assembly of the engine during an engine disassembly or assembly procedure. The support elements are configured to transfer any rotor assembly weight loads to an engine casing while a bearing support of the rotor assembly is absent or removed.

CROSS REFERENCED TO RELATED APPLICATION

The present application is a divisional application of U.S. patentapplication Ser. No. 13/036,075 filed on Feb. 28, 2011, the entirecontent of which is herein incorporated by reference.

TECHNICAL FIELD

The described subject matter relates generally to gas turbine enginesand more particularly, to rotor centralization in gas turbine engineassembly.

BACKGROUND OF THE ART

A gas turbine engine generally includes one or more rotors supported bybearing structures in the engine. During an engine maintenanceoperation, such as on-wing hot section inspections of an aircraftturbine engine, in some engines an aft engine portion including an aftshaft bearing support structure is removed to provide access to theinterior of the engine. Once the bearing support is removed, however,the rotor which the bearing supports tends to droop down, under its ownweight, at the unsupported side to thereby create misalignment relativeto the remaining support structures within the engine. This misalignmentmay cause damage to the rotor components at tight fit locations and mayalso cause difficulties during re-assembly of the engine.

Accordingly, there is a need to provide an improved approach.

SUMMARY

In accordance with one aspect, the described subject matter provides amethod for supporting a gas turbine rotor assembly during engineassembly/disassembly, the rotor assembly having a central shaftextending substantially horizontally and supported by at least onebearing support structure, the method comprising: a) extending at leastone elongate support element radially through an opening defined in acasing of the engine, the casing surrounding the rotor assembly; b)contacting the at least one support element with a portion of the rotorassembly at a location spaced apart from the at least one bearingsupport structure; and c) rigidly connecting the at least one supportelement to the casing of the engine, wherein the at least one supportelement is configured and positioned such that the at least one supportelement and the at least one bearing support structure cooperate tocentralize and at least partially support the weight of the rotorassembly when a second bearing support structure of the engine isabsent.

In accordance with another aspect, the described subject matter providesan apparatus for supporting a rotor assembly in a substantially centeredposition in a gas turbine engine, the apparatus comprising: at leastthree elongate support elements each extending radially through anopening defined in an exterior of a casing surrounding the rotorassembly, an inner end of each support element contacting with aperiphery of the rotor assembly, the support elements each beingconnected at an outer end thereof to said exterior of the casing, the atleast three support elements thereby configured to centralize andsupport the rotor assembly when a bearing support structure of the rotorassembly is absent.

In accordance with a further aspect, the described subject matterprovides a method for supporting first and second rotor assembliesduring engine assembly/disassembly, the second rotor assembly having ahollow central second shaft extending substantially horizontally andsupported by at least at one bearing support structure, a first centralshaft of the first rotor assembly co-axially extending through thehollow central second shaft of the second rotor assembly, opposite frontand aft end portions of each of the first and second shafts beingsupported by a respective front support structure and an aft supportstructure within the engine during engine operation, the methodcomprising: a) radially extending three rigid elongate support elementsthrough respective openings circumferentially spaced apart in a casingsurrounding the first and second rotor assemblies, to lock the secondrotor assembly in a substantially horizontal and centered position inthe engine; and b) inserting at least one spacer in an annulus betweenthe first and second shafts to support the first rotor assembly on thesecond rotor assembly, thereby locking the first and second shafts inthe coaxial relationship.

Further details of these and other aspects of the described subjectmatter will be apparent from the detailed description and drawingsincluded below.

DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying drawings depicting aspects ofthe present invention, in which:

FIG. 1 is a schematic cross-sectional view of a turbofan gas turbineengine according to one embodiment of the present description;

FIG. 2 is a simplified schematic transverse cross-section of theturbofan gas turbine engine taken along line 2-2 of FIG. 1;

FIG. 3 illustrates an enlarged area of the engine, as circled andindicated by numeral 3 in FIG. 1, showing the adjustable connection ofthe bolt to the casing; and

FIG. 4 illustrates an enlarged area of the engine, as circled andindicated by numeral 4 in FIG. 1, showing a spacer placed between thecoaxial high and low pressure spool shafts when a bearing structure isremoved, according to another embodiment.

DETAILED DESCRIPTION

FIG. 4 illustrates an enlarged area of the engine, as circled andindicated by numeral 4 in FIG. 1, showing a spacer placed between thecoaxial high and low pressure spool shafts when a bearing structure isremoved, according to another embodiment.

Referring to FIG. 1, a turbofan gas turbine engine which is taken as anexemplary application of the described subject matter, includes a fancase or engine nacelle 10, a core casing 13, a low pressure spoolassembly 15 which includes a fan assembly 14 and a low pressure turbineassembly 18 connected by a central shaft 12, and a high pressure spoolassembly 23 which includes a high pressure compressor assembly 22 and ahigh pressure turbine assembly 24 connected by a central shaft 20. Thecore casing 13 surrounds the low and high pressure spool assemblies 15,23 defining a main fluid path (gas path) therethrough (not numbered). Inthe main fluid path there is provided a combustor 26 to generatecombustion gases in order to power the high and low pressure turbineassemblies 24, 18.

The shaft 20 of the high pressure spool assembly 23 is hollow to allowthe shaft 12 of the low pressure spool assembly 15 to extendtherethrough such that the shafts 12 and 20 and thus the low pressureand high pressure spool assemblies are disposed substantially coaxiallywithin the engine. The common rotation axis of the shafts 12 and 20defines the main central axis 30 of the engine.

A bearing support structure 16 which may be part of an intermediate case(not indicated) of the engine, supports the respective shafts 12 and 20at a front or upstream portion thereof and a bearing support structure32 which may be part of a mid turbine frame 28 positioned between thehigh pressure turbine assembly 24 and the low pressure turbine assembly18, supports the respective shafts 20, 12 at an aft or downstreamportion thereof. Therefore, the bearing support structures 16 and 32assure the centered position of both shafts 12 and 20, and thus the lowand high pressure spool assemblies within the engine.

Referring to FIGS. 1-4, one embodiment is shown for a method andapparatus for temporarily supporting or locking a gas turbine rotorassembly such that the respective shafts 12 and 20 are in theirsubstantially centered positions within the engine during engineassembly/disassembly when the engine is disposed substantiallyhorizontally and one of the bearing support structures 16, 32 is absent.During an engine maintenance operation such as in a hot sectioninspection, an aft portion of the engine including the mid turbine frame28 is removed to provide rear end access to the interior of the engine.The shafts 12 and 20, particularly the aft portion thereof, tends todrop down, causing deviation from the main central axis 30 of theengine, which is not desirable and should be avoided. Therefore, anapparatus for temporarily supporting or locking the shafts 12 and 20 intheir substantially centered position within the engine is desired.

The apparatus according to this embodiment includes three rigid elongatesupport elements such as metal bolts 34 which radially extend throughrespective openings 36 circumferentially spaced apart in the core casing13, to lock the high pressure spool assembly 23 in a substantiallyhorizontal and centered position in the engine. At this moment, thesubstantially horizontal and centered position of the shafts 12, 20 andthus the low and high pressure spool assemblies 15, 23 are assured bythe bearing support structures 16 and 32. Each of the bolts 34 isreleasably secured to an outside of the core casing 13. For example, anut 35 is welded to the outside of the core casing 13, aligning witheach of the openings 36 for engagement with a threaded section 38 ofeach bolt 34.

The threading engagement of the threaded section 38 of the bolt 34 withthe nut 35 also functions as a means for adjusting the radial positionof each bolt 34 relative to the core casing 13 in order to ensure a firmcontact between an inner end of the bolt 34 and the high pressure spoolassembly 23 which is represented by the high pressure compressorassembly 22 in FIG. 2. The threaded section 38 located in an outer endportion of each bolt 34, may have a diametric dimension larger than thediameter of the remaining section of the bolt in order to allow the bolt34 to conveniently extend through the opening 36 in the core casing 13.

The three bolts 34 may be disposed in a same axial location of theengine and may in combination define a plane as shown in FIG. 2,substantially perpendicular to the central axis 30 of the engine.Alternatively, the three bolts 34 may be disposed in different axiallocations of the engine. The axial location of the bolts 34 may beselected differently for different types of engines. For example, in theembodiment shown in FIG. 1, the bolts 34 are positioned in an axiallocation such that the inner ends of the bolts 34 are in contact withthe high pressure compressor assembly 22, such as in contact with acompressor platform (not numbered) thereof The compressor platforms incombination define an inner surface of the main fluid path of the rotorassembly.

The one or more openings 36 in the core casing 13 which receive therespective bolts 34 to radially extend therethrough, may be existingports defined in the core casing 13 such as a borescope port, if one ormore such existing ports are available at a desirable axial location(s)of core casing 13. Otherwise, openings 36 dedicated for temporarilyreceiving the respective bolts 34 are provided in the selected locationsof the core casing 13 and are sealingly covered during engine operation.

The axial location of the bolts 34 should also be convenient for accessfrom the outside of the core casing 13 to place and remove the bolts 34.In the embodiment illustrated in FIG. 1, an aft section of the enginenacelle 10 is either openable or removable from the remaining section ofthe nacelle 10 which is mounted to the wing of an aircraft.

It should be noted that one of the bolts 34 as shown in FIG. 2, isdisposed substantially in a vertical direction, which may not benecessary. However, if one of the bolts 34 is vertically disposed underthe high pressure compressor assembly 22 as in an inverted image of FIG.2, the bolt 34 in combination with the bearing support structure 16 willfully support the shaft 20 and thus the high pressure spool assembly 23in its substantially horizontal and centered position within the enginewhen the bearing support structure 32 is removed. Therefore, the othertwo bolts 34 may not be in use. This single bolt support arrangement maybe desirable in some circumstances according to various enginestructures and/or tasks.

A spacer, for example a sleeve 40 according to this embodiment, may beprovided to be inserted in an annulus 42 between the coaxial shafts 20and 12 to support the inner shaft 12 on the outer shaft 20 in theircoaxial relationship, thereby maintaining the low pressure spoolassembly 15 in the substantially horizontal and centered position withinthe engine when the bearing support structure 32 is removed. The spacer40 may have a small section (not numbered) having a thickness to alloweasy insertion of the small section into the annulus 42 whilesubstantially maintaining the coaxial relationship between the shafts 12and 20. The sleeve 40 may further include a large section (not numbered)having a diametric dimension larger than the diameter of the hole of theshaft 20, to prevent over-insertion of the sleeve 40 from the aft endportion of the shaft 20 and to facilitate easy removal of the sleeve 40.

It should be noted that placement of the bolts 34 and the sleeve 40 fortemporarily locking the substantially horizontal and centered positionof the respective shafts 20 and 12 within the engine during an enginemaintenance operation, should be completed before removing the bearingsupport structure 32 and the bolts 34 and the sleeve 40 should bemaintained in position until the maintenance operation is completed andthe bearing support structure 32 is placed back in position.

In circumstances wherein the bearing support structure 16 which islocated at the front portion of the high and low pressure spoolassemblies 23, 16 is to be removed, the sleeve 40 should be placed inthe annulus 42 between the inner and outer shafts 12, 20 at a front endportion of the shafts 12, 20. If use of a sleeve 40 is not applicabledue to engine structure, individual spacers such as three spacer blocks(not shown) instead of the sleeve 40 may be used.

The method and apparatus described above for temporarily locking and/orsupporting the rotors of a gas turbine engine in their substantiallycentered position within the engine are not limited to use in an enginemaintenance operation. The described method and apparatus may also beused for engine production assembly. The described method and apparatusmay allow an engine assembly procedure in a more “ergonomic friendlyposition” with regard to assembly steps conducted and assembly platformsused in a horizontal engine assembly procedure with respect to those inan vertical engine assembly procedure.

The above description is meant to be exemplary only, and one skilled inthe art will recognize that changes may be made to the embodimentsdescribed without departure from the scope of the described subjectmatter. For example, although a turbofan gas turbine engine havingcoaxially positioned high and low pressure spool assemblies has beenused as an exemplary application of the described method and apparatus,the method and apparatus may be applicable to various types of gasturbine engines. The bearing support structures may not necessarily beassociated with a mid turbine frame or an intermediate case but could beapplied to any support structures depending on the particular enginestructure for which the described method and apparatus are used. The useof elongate support elements such as the metal bolts and the use ofspacers such as the sleeves, may not necessarily be combined and can beapplicable one without the other depending on the particular enginestructure in which they are used. Although a horizontal arrangement isdiscussed, the approach may likewise be applied to a gas turbine enginevertically-oriented during assembly or maintenance. Still othermodifications which fall within the scope of the described subjectmatter will be apparent to those skilled in the art, in light of areview of this disclosure, and such modifications are intended to fallwithin the appended claims.

The invention claimed is:
 1. A method for supporting a gas turbine rotorassembly during engine assembly/disassembly, the rotor assembly having acentral shaft extending substantially horizontally and supported by atleast one bearing support structure, the method comprising: a) extendingat least one elongate support element radially through an openingdefined in a casing of the engine, the casing surrounding the rotorassembly; b) contacting the at least one support element with a portionof the rotor assembly at a location spaced apart from the at least onebearing support structure; and c) rigidly connecting the at least onesupport element to the casing of the engine, wherein the at least onesupport element is configured and positioned such that the at least onesupport element and the at least one bearing support structure cooperateto centralize and at least partially support the weight of the rotorassembly when a second bearing support structure of the engine isabsent.
 2. The method as defined in claim 1 wherein the at least onesupport element comprises three support elements, the three supportelements being equidistantly spaced about the rotor assembly to therebycooperatively fix the rotor assembly in the substantially centered andhorizontal position within the engine.
 3. The method as defined in claim1 wherein an inner end of the at least one support element contacts therotor assembly.
 4. The method as defined in claim 1 wherein the at leastone support element contacts an annular inner gas path surface of therotor assembly.
 5. The method as defined in claim 2 further comprising astep of adjusting a radial effective length of each of the supportelements relative to the casing before connecting the respective supportelements to the casing.
 6. The method as defined in claim 1, wherein theat least one support element is connected to an outer side of thecasing.
 7. The method as defined in claim 1, wherein an outer end of theat least one support element is connected to the casing.
 8. The methodas defined in claim 2 further comprising the step of adjusting saidsecond bearing support structure so that it does not support the rotorassembly.
 9. The method as defined in claim 2 further comprisinginstalling said second bearing support structure within the engine tosupport the rotor assembly during an engine assembly procedure, and thenremoving said support elements from said rotor assembly contact.